The invention relates to a guide unit comprising at least one guide rail, optionally a rectilinear guide rail, this guide rail having a longitudinal axis and a rail profile with at least one track, also comprising at least two guide carriages guided on the at least one track of the guide rail with mutually facing ends and a covering means for covering the guide rail at least in a longitudinal portion of the guide rail between the two mutually facing end parts of the at least two guide carriages.
The covering part covering the guide rail protects the guide rail from contamination in guide units of this type.
It is known to use bellows as covering means; sheet metal angles are also conceivable.
It is the object of the invention to provide a covering means which is improved with respect to ITS production and its handling when being fitted into the guide unit.
To achieve the above object, it is proposed according to the invention that the covering means makes a driving connection with the at least two guide carriages for common movement therewith and has a substantially rigid configuration in the axial direction between the two mutually facing ends at least over a portion of its longitudinal dimension.
In particular, it is intended that the covering means, at least over a portion of its longitudinal dimension, forms a covering means profile which approximately follows the rail profile at a distance from itxe2x80x94when viewed in a section orthogonal to the longitudinal axis. The covering means can define a substantially closed profile cavity between the rail profile and the covering profile, which contains the at least one track of the guide rail extending between the two guide carriages.
The profile cavity can be sealed in that the profile cavity is sealed, optionally substantially tightly by formation of a narrow gap and/or contact zone between the guide rail and the covering means. This seal of the profile cavity can, on the one hand, be used to prevent soiling of the guide rail from the surrounding space and, on the other hand, also help to prevent the discharge of lubricant and to prevent the lubricant used to lubricate the guide carriage and, in particular, the points of engagement of the guide carriage with tracks from issuing into the surrounding space. Both requirements arise in many applications of the guide unit, particularly if the guide unit is used in robot construction, in machine tool construction, in assembly machine construction and the like.
A frequent design of guide carriage is based on the principle that the guide carriage surrounds a guide rail, which is approximately rectangular in cross-section, in the form of a U, so the transverse web of the U-shaped guide carriage opposes a top face of the guide rail whereas the two outer arms of the U each oppose one lateral face of the guide rail, and a base of the guide rail opposing the top face is designed to be fastened on a carrier. Guidance can be effected by endless races of antifriction members arranged with a respective load-transmitting row of antifriction members in a track of the guide carriage and in a track of the guide rail. Balls, needles and rollers and the like can be used as antifriction members. With a design of this type, the covering means profile will preferably be constructed as a U-profile, wherein the ends of the arms of the U of the covering means profile can rest in a sealing manner on the guide rail.
The covering means profile can be assembled from at least two partial profiles following one another in a circumferential direction round the longitudinal axis. xe2x80x9cAssembledxe2x80x9d means that the partial profiles can be produced separately and rest with their rims or edges against one another. However, xe2x80x9cassembledxe2x80x9d also means that the U-profile parts adjoin one another in one piece or are connected to one another in the manner of a hinge.
If partial profiles of the covering means profile following one another in the circumferential direction are articulated to one another round hinge axes parallel to the longitudinal axis, then it is possible to mount and dispatch the covering means profile in an approximately laid-flat state, so storage space and transport space are saved. A further advantage is that laid-flat covering means profiles can be fitted on site even under restricted spatial conditions, for example if a table is already mounted on two or more guide carriages following one another. In this case, a laid-flat covering means profile can be introduced in laid-flat form through a gap between guide rail and table and can then be caused to cover the guide rail by pivoting the partial profiles round the hinge pins.
It is conceivable that the covering means profile is assembled from at least two covering profile portions adjoining one another in the longitudinal direction.
Exact fixing of the length of the covering means profile is unnecessary if the covering means profile has length compensating means for adaptation to variations in spacing between the two guide carriages.
The covering means, in the vicinity of at least one guide carriage, can have a covering means joining element for producing the driving connection to the respective guide carriage. There are a number of alternative designs for this. It is basically conceivable to mount the covering means profile on the associated guide carriage on its lateral faces extending parallel to the longitudinal direction, for example by clipping. It should be noted with this solution, however, that the covering means profile, if it is resting against a transverse web of a U-shaped guide carriage, could impair the connection between the guide carriage and the table. A preferred embodiment therefore proposes that the covering means profile is accommodated within the contour of the guide carriage.
The covering means profile can be constructed at one or both ends with a covering means joining element for joining to the respectively associated guide carriage. The joining elements could both be mounted rigidly on the covering means profile. Therefore, the covering means can only be used for normal solutions, however, in which the spacing between successive guide carriages is predetermined. The spacing between successive guide carriages often varies. To allow for such varying spacing, there are also various solutions: for example, the covering means profile can be assembled from two covering profile portions which are each connected only at one end to a covering means joining element. Covering profile portions of this type with a covering means joining element arranged rigidly thereon, for example with the maximum necessary length, can be injection moulded from plastics material and one or both covering profile portions can then be shortened at the end remote from the respective covering means joining element so the sum of the lengths of the two covering profile portions corresponds to the spacing between succeeding guide carriages. A coupling part, optionally in conjunction with a seal, can then be arranged at the abutting ends of the two covering profile portions.
However, the covering means joining elements and the covering means profiles can also be produced separately. This separate production affords the advantage that the covering means profile can then be prepared as piece or bar goods and the length required in each case can be cut from it. This allows simple production, for example by intrusion or extrusion. The covering means joining element can be connected to the covering means profile by pushing them together. Simple length compensation can also be achieved in this way. To allow handling of this type, the covering means joining element will preferably be constructed with a driving part and a profile gripping part, the latter interacting with the covering means profile. The profile gripping part can be constructed for contacting the exterior of the covering means profile or for interacting with the interior of the covering means profile.
The profile gripping part can be designed to straddle the covering means profile. This is of particular interest if the covering means joining element has only small dimensions in the direction of the longitudinal axis as the covering means joining elements can also be fitted easily in restricted spatial conditions.
It is possible that a clasping means resting externally against the covering means profile is provided for securing the covering means profile resting externally against the profile gripping part on the profile gripping part. The clasping means can have an approximately U-shaped configuration.
The covering means joining element can comprise, as fastening part, a fastening flange to be screwed or clipped on an end face of a guide carriage substantially orthogonal to the longitudinal axis. In an embodiment which is preferred in terms of manufacture and fitting, a respective covering means joining element is arranged on each of two guide carriages directly following one another, at the mutually facing ends thereof, and at least one separate covering profile portion extends between the two covering means joining elements.
If the covering means profile between two successive guide carriages is very long owing to the large spacing therebetween, it may be necessary to stabilise the covering means profile at a central position between the two guide carriages, particularly if a tight, in particular lubricant-tight covering is required. The stabiliser can at the same time form a coupling means between two covering profile portions directly adjoining one another.
If a covering means profile and a covering means joining element are produced separately and only connected to one another at a later stage, in particular as they are fitted into the guide unit, the cohesion during operation can be promoted if the profile gripping part can be locked to the covering means profile.
Length compensation which, in particular, is to allow fine adaptation of the covering means to the spacing between successive guide carriages can be achieved in that the length compensating means is formed by a sliding section on a covering means joining element and/or between two covering profile portions adjoining one another.
Lubricant for lubricating the at least one track can be provided within the covering means. If the track is lubricated in this way, it may be unnecessary to supply lubricant to the guide positions of the guide carriages running on the respective track. The advantage then arises that lubricant supply systems within the guide carriages can be avoided under certain circumstances. This advantage is significant in so far as it may be difficult to provide a lubricant supply within guide carriages owing to the restricted space, particularly in the case of guide carriages constructed with races of antifriction members.
There is generally abundant space for accommodating lubricants within the covering means, so long-term lubrication or even service-life lubrication can be supplied. However, refilling with lubricant should not be ruled out. In this case, nipples or the like can easily be provided on the covering means profile.
High-viscosity lubricating greases as well as low-viscosity lubricating oils can be used as lubricant. The lower the viscosity of a lubricating oil, the more careful the seal obviously has to be.
If lubrication is to be carried out using lubricating oil, it is possible to provide at least one porous lubricant-containing oil distributor within the covering means. This oil distributor can make lubricant delivery contact (lapping contact) with a track of the guide rail.
If lubricant is also required within the guide carriage, the lubricant within the covering means can have access to lubricant-demanding positions within the guide carriage.
If the covering means, for achieving a good seal, is making frictional contact with contact zones of the guide rail, it may be advantageous for the service life of the covering of the guide rail if the lubricant within the covering means has access to a narrow point or a contact zone between the guide rail and the covering means.
The oil distributors can be extended basically over the entire length of the spacing between two successive guide carriages. As a result, there is already a large quantity of lubricant in the oil distributor, which may be adequate for long-term lubrication or service-life lubrication. However, the oil distributor should also be able to make a lubricant-conveying connection to a storage space for unbound lubricant. In this way, the quantity of lubricant available is further increased and the time interval between successive replenishments with lubricant is increased. If an oil distributor, for example in strip form, is provided on the covering means profile, an internal bias in the covering means profile or also a bias applied by external biasing means can ensure that the oil distributor is invariably pressed into lubricant-delivering contact with the track.
If the spacing between successive guide carriages is very long, it may be desirable to allow the oil distributorxe2x80x94for example through recessesxe2x80x94to rest against the track only over a portion of this length in order to prevent excessive frictional force in this way.
The parts of the covering means can be injection moulded, cast, extruded, drawn or bent from plastics material or metal.
With the aforementioned guide carriages comprising races of antifriction members in a U-shaped carriage member, the carriage member was formerly constructed with a sealing element at both ends, so that the lubricant within the carriage member was restricted to the length region of the carriage member and no lubricant passes to the respective guide rail portions not covered by the carriage member. With the construction according to the invention, it is possible to dispense with the sealing elements of the guide carriages facing the intermediate space between successive guide carriages if the space enclosed by the covering means is constructed in a lubricant-tight manner.
It is possible to provide, on the covering means, at least one sliding face which makes sliding engagement with a slideway of the guide rail. In comparison with the alternative embodiment in which the covering means is guided on the guide rail only indirectly via the guide carriage, the solution with a sliding face on the covering means and a slideway on the guide rail, which make sliding engagement, affords the advantage that, even with very great spacing between two successive guide carriages, deformations of the covering means can be avoided if it is brought into sliding engagement with the slideway of the guide rail at one or more points. Owing to the production of this sliding engagement, the covering means can be structurally weaker in design without running the risk of deformation, even if very great distances between successive guide carriages are to be bridged over.
The slideway with which one or more sliding faces of the covering means is to be brought into sliding engagement, can be formed by a track of the guide rail, in other words a track on which the guide carriage itself runs in a rolling or sliding manner.
However, as peripheral portions of greater size, not required by the tracks or track, are available at the cross-sectional contour of the guide rail, it is also conceivable for the slideway for engagement of a sliding face of the covering means to be separated from the track or the tracks for the guide carriages. The first option affords the advantage that it is not necessary to take further steps on the guide rail for forming the slideway or slideways apart from the track or tracks already required for guiding the guide carriage or carriages. The second option affords the advantage that track wear is avoided owing to the sliding engagement with one or more sliding faces of the covering means and lubrication of the track can be focused merely on the requirements of guide carriage guidance.
In the embodiments of the invention discussed hitherto, it was hinted that the covering means could be connected to at least one of the guide carriages adjoining it by fastening it on the respective guide carriage.
It is proposed in an embodiment which is preferred under certain circumstances, however, that the covering means merely makes pressure-transmitting contact with at least one of the guide carriages; in other words: the driving connection is provided by pressure transmitting contact. To understand this step, it should be remembered that two successive guide carriages, between which a covering means is to be placed, are frequently already connected to one another by a bridge, a table or another object and are therefore spaced apart so that the covering means does not have to act as a spacer in any case. Under these circumstances, adequate positioning of the covering means is ensured if the covering means on the one hand is guided on the guide rail by at least one, preferably several sliding faces and on the other hand, merely makes pressure-transmitting contact with the mutually facing end parts of the guide carriage. This embodiment has the further advantage that the mounting of the covering means is greatly simplified; it is merely necessary to bring the covering means with its guide face or its guide faces into sliding engagement with the slideway or the slideways of the guide track and to bring together the guide carriages with their mutually facing end parts until they contact the respectively associated ends of the covering means and to fix the mutual spacing thus obtained. The covering means can be isolated in terms of transverse force from at least one of the guide carriages; it is preferably isolated in terms of transverse force from both guide carriages. The expression xe2x80x9cisolated in terms of transverse forcexe2x80x9d denotes that the respective end of the covering means is displaceable at least slightly in the transverse direction to the guide rail in relation to the associated end part of a guide carriage. This prevents double passes which might otherwise occur if, on the one hand, the covering means is guided directly on the guide rail by sliding face slideway engagement and, on the other hand, one or both ends of the covering means are fastened on one or both guide carriages.
If the spacing between two successive guide carriages is predetermined by an object connected to both guide carriages, for example by a table, it must be ensured, for optimum enclosure of the respective guide rail portion located between the two guide carriages, that the length of the covering means corresponds as exactly as possible to the internal clearance between two mutually opposed end faces of the two guide carriages, in particular the spacing between the end faces, turned to one another, of end parts of the two guide carriages. It is therefore recommended that the covering means rests with a bias against the mutually facing end parts of the guide carriages. It is then possible elastically to shorten the length of the covering means in adaptation to the spacing between the two guide carriages determined by extraneous means and simultaneously to ensure close contact between the ends of the covering means and the end faces of the guide carriages.
Depending on the application, it is advisable to supply the sliding face of the covering means or/and the slideway of the guide rail with lubricant. If the slideway is identical to at least one track of the guide rail and if the track, in turn, is to be lubricated, smooth running of the sliding face of the covering means can be ensured by lubrication of the track.
If there is sufficient spacing from the guide rail to be covered, the covering means provides adequate space for accommodating a supply of lubricant if the track of the guide carriage is to be lubricated or if a slideway for the covering means is to be lubricated or also if specific functional parts within a guide carriage are to be lubricated, for example a race of balls or a race of rollers. The term xe2x80x9csupply of lubricantxe2x80x9d at this point covers the case, on the one hand, where a lubricant store is to be accommodated within the covering means for a prolonged period, possibly for the entire service life of the guide unit, and, if necessary, also the distributor, in order to bring the lubricant to lubricant-demanding positions. The term xe2x80x9csupply of lubricantxe2x80x9d at this point should also cover the possibility that lubricant, whether lubricating oil or lubricating grease, is continuously supplied from the exterior, for example via a flexible line, to the covering means and distributors are provided within or on the covering means in order to guide the lubricant to the respective lubricant-demanding positions.
The covering means can consist of at least two covering means parts adjoining one another in the direction of the longitudinal axis. This means inter alia that at least one end of a covering means close to the guide carriage can be produced separately from the part of the covering means bridging the remaining length. The part of the covering means close to the guide carriage can be adapted to its function of contact with the guide carriage, and the part of the covering means intended to overlap the remainder of the guide rail can be produced most simply as a covering means profile having a constant cross-section over its entire length and can therefore be produced easily to any length by production processes such as extruding, intruding, extrusion, drawing or bending.
Furthermore, the term xe2x80x9cat least two covering means parts adjoining one anotherxe2x80x9d should also cover the case where a part of the covering means covering the majority of the length between two successive guide carriages and two covering means end pieces which are adapted to their contacting function with respect to the guide carriage, follow one another in the longitudinal direction. The case should also be covered where two or more parts of the covering means of greater length follow one another, for example if a store of standard length pieces of the covering means is available and a specific length between two successive guide carriages is to be bridged by a series arrangement from this store. It is then necessary to measure only the predetermined spacing between two guide carriages and to divide it by the standard length of the available parts of the covering means. The resultant number is the number of parts of covering means required. According to the remainder, a further covering means part is shortened and also included in the series arrangement. This method of assembling a covering means is possible, in particular, if sliding faces of the covering means are provided in each case in the region where two successive covering means parts abut. The problem of tolerance compensation can then be achieved by providing biasing means on at least one of the covering means parts so that the series of covering means parts can be compressed in adaptation to the respective clear length between two successive guide carriages.
According to a common embodiment, the covering means comprises at least one covering means profile and at least one covering means end piece which is designed to rest against a guide carriage. A compressible spring means can be provided between the covering means profile and the covering means end piece. This spring means can be provided, in particular, on the covering means end piece which cannot be produced by extrusion, drawing or the like in any case, but has to be produced by a casting or injection moulding process. With a casting or injection moulding process of this type, the spring means can be produced coherently from the material of the covering means end piece in one piece with it.
If the covering means consists of at least two covering means profile portions which follow one another in the direction of the longitudinal axis, these covering profile portions can be connected to one another by a coupling piece. This does not necessitate special coupling measures on the covering profile portions. It is merely necessary to design the coupling piece for coupling and to plug the covering profile portions together by means of the coupling piece. The coupling piece can therefore be a coupling piece which is separate from the two covering profile portions, and any spring means required can also be provided on the coupling piece and can, in turn, be shaped from the material of the coupling piece in one piece with it by casting or injection moulding. To sum up, it can be stated that the covering means can comprise at least one covering means profile and at least one plug-on part. xe2x80x9cPlug-on partxe2x80x9d in this connection therefore denotes coupling piece as well as covering means end piece. In any case, at least one plug-in pocket can be formed on the plug-on part to receive the associated end of a covering means profile. It is obviously desirable to shape the plug-in pockets on a coupling piece and on a covering means end piece so as to be identical in profile so that each plug-on piece fits each covering means profile.
The covering means profile can be designed as a hollow wall profile. Production of the covering means profile as a hollow wall profile affords the advantage that the covering means profile is stiffened without a significant increase in weight. This stiffening is desirable both with respect to the dimensional stability of the covering means profile against the action of gravity and with respect to improved protection of the guide rail from impacts from the exterior.
Production of a covering means profile as a hollow wall profile also affords various possibilities for plugging together plug-on parts such as covering means end pieces and coupling pieces on the one hand and covering means profiles on the other hand. Thus, at least one plug-in projection can be provided on a plug-on part for plugging into a hollow profile chamber of a hollow wall profile. The sliding face of the covering means for sliding on a slideway of the guide rail can basically be formed directly on a coupling piece or a covering means end piece or a covering means profile.
If the sliding face of the covering means is formed by a separate sliding block, this has the advantage that the sliding block which is occasionally subjected to rapid wear can be exchanged without having to exchange the entire covering means. If a decision is made to mount the sliding face of a covering means on a separate sliding block or sliding blocks, these can therefore basically be mounted on covering means profiles or on associated plug-on parts, for example coupling pieces or covering means end pieces. It is advantageous, for practical reasons, if the sliding blocks are mounted on the covering means profile as holding profile means for receiving one or more sliding blocks can also be shaped easily during profile production.
A sliding block can basically extend over a substantial part or even over the entire length of the spacing between two successive guide carriages. For the sake of economy and to minimise frictional force, however, it is frequently desirable to provide sliding blocks of a substantially shorter length, for example in an end region of the covering means close to a guide carriage or even at a central point of the spacing between two guide carriages if it is necessary to prevent bending of the covering means. In the latter case, sliding blocks will preferably be mounted in the region of a coupling piece between two successive covering means profile portions participating in the formation of the covering means.
The sliding block can basically be designed as a lubricating member for lubricating a track or/and a slideway. For example, the sliding block can consist of a plastics material which, on the one hand, is hard enough to perform a stabilising guiding function but, on the other hand, is porous and contains solid or liquid lubricant in its pores.
However, the supply of lubricant is not linked to the use of the sliding block as a lubricating member; rather, it is possible to apply the lubricant to the respective lubricant-demanding surfaces without using the sliding block; it is thus possible that at least one lubricant dispenser is provided on the covering means next to a sliding block in the direction of the longitudinal axis, this lubricant dispenser being suitable for supplying lubricant to a track or/and a slideway. In this case, the material properties of the lubricant dispenser can be adapted specifically for the storage and delivery of lubricant without reference to the function of guidance.
The covering means can be provided with longitudinal sealing strips which are arranged opposite the guide track in the sealing position and, together with the guide rail, form an enclosure for at least one track or/and at least one slideway. The term xe2x80x9csealingxe2x80x9d here denotes both sealing by physical contact and sealing in which the covering strips extend so close to the respective surface of the guide rail that the remaining gap is small enough to prevent the admission of dirt, without sliding contact. Even if the covering means is guided directly on the guide rail due to interaction of sliding faces and slideways independently of the guide track, perfect sealing is expected as the risk of a loss of seal due to a double fit is reduced.
As already mentioned hereinbefore, the covering means frequently has a U-shaped configuration in order to cover a guide rail with head part, lateral faces and foot part. It will be adequate and even desirable for many applications to allow the lateral arms of the covering means to extend not right to the foot part and not to a base carrying the foot part.
On the other hand, however, situations cannot be ruled out in which the lateral parts of the covering means will extend down to the foot part or to a base carrying the foot part. For this purpose, holding means can be provided on the covering means for the mounting of covering supplements, thus affording the advantage that a substantial part of the covering means, namely the U-shaped profile member, can be retained and, if necessary, only needs to be supplemented by the covering supplement. These covering supplements are not only provided and suitable for covering an uncovered foot part of the guide rail and for providing a seal from a base carrying the guide rail, but it is also conceivable to design the covering supplements in such a way that they provide a lateral covering for a guide carriage combined with the covering means. A covering supplement can also be designed as a seal from an object, in particular table, carried by at least one guide carriage. It is thus possible, with a modular system having a relatively small number of standard parts, to achieve a more or less complete enclosure, as required, which covers only parts of the guide rail as required or encloses the entire space between a base carrying the guide rail and an object carried by the guide carriage, possibly also in the region of the guide carriage itself.
The holding means for the mounting of covering supplements can be designed as a supplement holding profile which, in turn, is mounted on a covering means profile where it can easily be shaped by corresponding design of drawing dies, extrusion dies, or the like during production of the covering means profile.
Adapters which can be brought into engagement with a holding profile of the covering means on the one hand and with a coupling profile of the covering supplement on the other hand, for example by sliding them in axially or by snapping or hooking them in, can be provided for connecting covering supplements to a covering means profile. In particular, adapters of this type should be so designed that they can be used selectively for connecting the covering means to various covering supplements.
Reference has already been made to the possibility of also using a covering means to accommodate a supply of lubricant. The possibility of accommodating, in the covering means, a lubricant duct extending in the longitudinal direction of the guide rail should, however, also be added. This possibility of accommodating a lubricant duct exists, in particular, if the covering means is produced with covering means profiles produced by extrusion, intrusion or drawing.
If a lubricant duct of this type is provided, it can make a lubricant-conveying connection with a lubricant delivery point or/and with a track or/and with a slideway or/and with a lubricant joining orifice of at least one guide carriage. For example, the lubricant delivery point can be via a flexible hose with a lubricant pump or a lubricant press or a lubricant store subjected to gravity.
As the guide carriages frequently have, at their end parts, a central lubricant joining orifice into which a lubricating nipple has generally been inserted in the past, it is advisable to position a lubricant duct in such a way that, after assembly of a covering means with two successive guide carriages, it is axially aligned with the central, axially orientated lubricant joining orifices of the guide carriages. The tight connection between the lubricant duct and the lubricant connections in the end pieces of the guide carriages can have a blunt configuration such that, owing to the connection between lubricant duct of the covering means on the one hand and the lubricant connections of the guide carriage on the other hand, the isolation, in terms of transverse force, of the covering means and the guide carriage is not eliminated.
The connection between the lubricant duct in the covering means and a lubricant store can be produced, for example, in the region of an end piece or/and a coupling piece. There is an unrestricted possibility for connection of a flexible hose or the like in the region of the coupling piece as the respective guide carriage is far removed there.
If the guide unit is connected to a linear drive which is to transport the guide carriage in the longitudinal direction of the guide rail or guide rails, this linear drive also frequently requires lubricant. This applies, for example, if a spindle drive, in particular a spindle drive with a ball nut is used as linear drive. A lubricant duct integrated into the covering means can also communicate with the lubricant supply of the linear drive in such cases.
The seal of an enclosed space created by the covering means in the environment of a guide rail is not quite completed by sealing strips extending in the axial direction of the guide rail. A seal is also required where the covering means abuts against a guide carriage. Sealing means can also be provided there. Furthermore, sealing means can also be provided where two successive covering profile portions abut with a coupling piece.
Every endeavour will be made to mount sealing means of this type on covering means end pieces or on coupling pieces, as the production of these parts most easily allows the simple mounting of sealing means.
The coupling pieces between successive covering profile portions already mentioned several times are relatively complicated shaped articles and they become even more complicated if, as already indicated, lubricant ducts and branches from these lubricant ducts also extend in the region of the coupling pieces. To simplify the shaping here, it is proposed that the coupling piece is assembled from two preferably identical mouldings which abut in a connecting plane orthogonal to the longitudinal axis.
The covering means can be a body which is closed in on itself; in particular, a covering means profile associated with the covering means can be rigid in itself, for example U-shaped. To simplify production of the covering means and to simplify installation of the covering means into a guide unit, however, the covering means can comprise a covering means profile with a plurality of profile wall parts which adjoin one another round the longitudinal axis in the circumferential direction and are articulated to one another. The profile wall parts can be constructed with hinge parts to allow the profile wall parts to pivot relative to one another round hinge axes parallel to the longitudinal axis. These hinge parts can be pivoted relative to one another and brought into an interlocking position in which the profile wall parts define a profile cross-sectional shape suitable for covering the guide rail. The hinge parts can be connected to one another by being pushed together axially or by hooking.